The vascular flora and floristic relationships of the Sierra de La Giganta in Baja California Sur, Mexico

Abstract

THE SIERRA DE LA GIGANTA IS A SEMI-ARID REGION IN THE SOUTHERN PART OF THE BAJA CALIFORNIA PENINSULA OF MEXICO. TRADITIONALLY, THIS AREA HAS BEEN EXCLUDED AS A SECTOR OF THE SONORAN DESERT AND HAS BEEN MORE OFTEN LUMPED WITH THE DRY-TROPICAL CAPE REGION OF SOUTHERN BAJA CALIFORNIA PENINSULA, BUT THIS CLASSICAL CONCEPT OF THE VEGETATION HAS NOT PREVIOUSLY BEEN ANALYZED USING FORMAL DOCUMENTATION. IN THE MIDDLE OF THE LAST CENTURY, ANNETTA CARTER, A BOTANIST FROM THE UNIVERSITY OF CALIFORNIA, BEGAN EXPLORATIONS IN THE SIERRA DE LA GIGANTA THAT LASTED 24 YEARS, SHE COLLECTED 1 550 SPECIMENS AND DESCRIBED SEVERAL NEW SPECIES FROM THIS AREA, BUT SHE NEVER PUBLISHED AN INTEGRATED STUDY OF THE FL ORA. OUR OBJECTIVES, HAVING DEVELOPED EXTENSIVE COLLECTIONS IN THE SAME AREA OVER THE PAST YEARS, ARE TO PROVIDE A COMPREHENSIVE SPECIES LIST AND DESCRIPTION OF THE VEGETATION OF THIS MOUNTAIN RANGE. WE FOUND A FL ORA OF 729 TAXA, POORLY REPRESENTED IN TREE LIFE-FORMS (3.1%), A MODERATE LEVEL (4.4%) OF ENDEMISM, AND THE DOMINANCE OF PLANTS IN THE SAMPLING PLOTS IS COMPOSED MAINLY FOR LEGUME TREES AND SHRUBS. ADDITIONALLY, USING A BIOGEOGRAPHICAL APPROACH, WE COMPARE OUR LIST WITH OTHER KNOWN LISTS OF PLANTS FROM 5 AREAS, 3 IN THE CAPE REGION, 1 IN THE SONORAN DESERT, AND OTHER IN THE THORNSCRUB AREA OF NW MEXICO. WE CONCLUDE THAT THE LA GIGANTA FL ORA HAS A MIXED COMPOSITION, PRIMARILY MADE UP OF PLANTS SHARED WITH THE LOWLANDS OF THE SOUTHERN CAPE REGION, BUT ALSO SHARE AN IMPORTANT PROPORTION OF THE FL ORA WITH THE DESERT MOUNTAINS OF THE CENTRAL PENINSULA AND SOME WITH THE SONORAN DESERTSCRUB OF MAINLAND MEXICO. CONSEQUENTLY WE SUPPORT THAT THE LA GIGANTA FL ORA IS PART OF A FL ORISTIC CONTINUUM ALONG THE VOLCANIC MOUNTAINS OF THE SOUTHERN PENINSULA THAT EVENTUALLY COULD BE CONSIDERED A NEW ECO-REGION IN THE SAME PENINSULAR LAND.